This invention relates to heat engines which are operated by the utilization of variations in volume of materials which are expanded and contracted when heated and cooled, and more particularly to a heat engine utilizing a non-compressible material.
Known as heat engines in the art are steam engines, external combustion engines, and internal combustion engines. Among them, the steam engines are bulky because they need a boiler, a condenser, etc. The external combustion engines are less developed because of technical difficulty. Thus, the internal combustion engines are most extensively employed. However, recently it has been pointed out that the internal combustion engines are sources of public nuisance generating air pollution, noise, and so forth. In order to overcome this drawback, a variety of methods to improve internal combustion engines have been proposed; however, these methods are still insufficient to completely eliminate the drawback. Since most of the internal combustion engines use fossil fuels, especially petroleum, the use of the internal combustion engines is liable to be affected by changes in fuel supply which have been caused recently. Accordingly, there is a strong demand for the development of novel heat engines which can replace the internal heat engines.
Thus, the Stirling cycle engine has been reconsidered in the course of developing these novel engines. This is an external combustion type gas engine which has been put into practical use hitherto and has the possibility of being practically used in some cases.
However, this engine needs considerably high technology in material and mechanical construction, and still has problems to be solved in combining it with load devices.
An ideal engine can satisfy a variety of requirements such as compactness, high efficiency, great output, and high durability. In order to provide such an ideal engine, it is necessary:
(1) to increase the engine rotational speed; PA1 (2) to increase the pressure of a fluid sealed therein; PA1 (3) to increase the compression ratio; PA1 (4) to increase the temperature on the high temperature side; and PA1 (5) to increase the efficiencies in heat exchange of the heater, the reheater, and the cooler.
However, these requirements involve the following problems.
In order to increase the rotational speed, it is necessary to increase the speed of movement of the gas. However, the heater, the reheater, and the cooler impose obstructions in the gas passage. Therefore, if the rotational speed is increased, the flow resistance is greatly increased, and the engine power is decreased. If, in order to overcome this difficulty, a gas, such as hydrogen or helium, which is of lower density than air is used, the problem of sealing arises in addition to the problem of increasing the pressure of the fluid sealed. Especially, sealing hydrogen gas is very difficult because it can pass through metal, and the problem of hydrogen embrittlement arises. The increase of the compression ratio may be achieved by making as small as possible the volume of the operating fluid when it is most compressed. However, in order to do so, it is necessary to decrease the internal volumes of the heater, the reheater, and the cooler and to decrease the internal volume of passages connecting these elements, which will lead to insufficient heat exchange. This is a problem to be solved prior to solving the problem of increasing the heat exchange efficiency. The increase of the temperature on the high temperature side is limited by the material to be used to approximately 800.degree. C. However, it is difficult to design the engine with small size and increased heat exchange rate, in the case where it is continually subjected to such a high temperature. In addition, the temperature increase will raise the problem of lubrication oil treatment; that is, a problem arises in the lubrication system.